The present invention relates to instruments that test the effectiveness of face mask personal respiratory systems.
When a person is in an area where exposure to toxic substances in the air is a possibility, the best protection often is to wear a protective face mask. A respiratory protective face mask is usually provided with a filter cartridge containing activated charcoal or other chemical absorber to remove toxic vapors by physical adsorption and/or chemical absorption. It is also provided with a particle filter comprised of a High Efficiency Particulate Air (HEPA) filter to remove toxic substances in particulate form. Military personnel fighting in a war zone where chemical and biological agents may be present often wear such respiratory protective face masks along with protective clothing. Emergency workers such as police and fire fighters who may enter areas containing toxic substances in the air also wear such protective face masks for personal protection purposes.
Although the filter cartridges used in respiratory protective face masks are quite efficient and capable of removing more than 99.97% of the toxic substances carried by air through the cartridge, the degree of protection provided by the face mask is limited by the air that may leak through the face seal between the mask and the skin of the face. Face-seal leakage is a critical factor in determining the effectiveness of the face mask for personal respiratory protection.
Commercial devices are currently available to detect the face seal leakage. One such device is made by TSI, Inc. of Shoreview, Minn., and is sold commercially under the trade name PORTACOUNT. It is comprised of a condensation nucleus counter (CNC) to count airborne particles in the ambient air and inside the face mask. The air inside the face mask is comprised of filtered air that has passed through the face mask filter and unfiltered air leaking through the face seal. The ratio of the airborne particle concentration outside the face mask to that inside indicates the relative amount of air in the face mask that has leaked through the face seal, hence the degree of protection that the face mask can provide. A concentration ratio of 1 means that air inside the face mask is the same as unfiltered air from the outside. The face mask, therefore, is not providing any protection to the wearer. In contrast, when there is no face seal leakage, and the cartridge filter removes 99.99% of all the particles passing through the filter, the ratio would be 10,000. The method of face mask testing using an instrument, such as a CNC, is known as a quantitative fit test. The concentration ratio measured as described above by such a device is referred to as a fit factor, or protection factor. A protection factor of 10,000 indicates a high degree of protection, while a protection factor of 1 means no protection.
While the currently available commercial PORTACOUNT has proven its usefulness for determining face-seal leakage, it has some shortcomings that have made an otherwise useful device less than fully satisfactory.
The PORTACOUNT as an instrument weighs about 2½ pounds. While it is not too heavy to be carried around, it is too large to be used as a portable instrument carried on the person for personal respiratory fit testing purposes. With the PORTACOUNT, a person wearing a face mask must be tested, usually with the help of another person, before the person goes into action where toxic substances may be encountered. Thus, before going into a war zone, a soldier must don the face mask and protective clothing, and be fit-tested before going into action. Similarly, a fire fighter also must undergo such fit-test before going into action. Once the person is fit-tested and goes into action, there is no means available to the person to determine if face seal leakage has developed or if the face mask is still effective in providing protection for the individual.